It is required by the future wireless communication and cellular system to increase the coverage and support higher transmission rate, which is a new challenge for the wireless communication technology. At the same time, the cost of system building and maintenance has become more expensive. With the increase in the transmission rate and communication distance, the problem of battery power consumption has become evident. Moreover, the future wireless communication will employ higher frequency, which will lead to more severe path loss and path attenuation. As a new technology, the relay technology has drawn more and more attention, and is viewed as a key B3G/4G technology. The traditional single hop link can be divided into a plurality of multi-hop links by the relay technology to shorten the distance, which greatly reduces the path loss and is helpful for increasing the transmission quality and enlarging the communication range, so as to provide services with higher speed and higher quality for the users.
FIG. 1 shows a structural diagram of a relay network. In the relay network, as shown in FIG. 1, a link between a user served by a relay station and the relay station is called an access link, a link between the relay station and a base station is called a backhaul link and a link between the user served by the base station and the base station is called a direct link.
When the user is located within the coverage of both the base station and the relay station, cooperative communication can be employed so that the base station and the relay station can jointly provide services for the user. FIG. 2 shows a schematic diagram of realization of cooperative communication in the relay network, by which system capacity and resource utilization rate can be increased.
Relay station Downlink cooperative retransmission is a cooperative communication method in the relay network. FIG. 3 shows a schematic diagram of relay station downlink cooperative retransmission. When the method is employed, as shown in FIG. 3(a) and FIG. 3(b), in the case that a receiving error occurs in the downlink transmission on the first transmission sub-frame direct link and a retransmission at the transmitter is required, the relay station performs a corresponding downlink retransmission on the retransmission sub-frame access link, to increase the transmission success rate of the downlink retransmission. The relay station downlink cooperative retransmission as shown in FIG. 3 is a cooperation method with low overhead and good compatibility, which does not need to make any change to the current system.
However, when the relay station performs cooperative retransmission for the downlink data which is on the direct link, it is possible that the quantity of available radio resources for data retransmission is different from that for the first transmission because the quantity of radio resources occupied by the Physical Downlink Control Channel (PDCCH) on the retransmission sub-frame has been changed compared with that on the first transmission sub-frame, which means that the retransmission transmitter needs to make corresponding adjustment during the physical layer processing to match the available radio resources on the current retransmission sub-frame. FIG. 4 shows a schematic diagram of possible problems that may occur during the relay station downlink cooperative retransmission. FIG. 4(a) shows the condition that the quantity of the available radio resources increases, while FIG. 4(b) shows the condition that the quantity of the available radio resources decreases, wherein the blank squares represent unavailable resources, the dotted squares represent radio resources available for data transmission, the squares filled with staggered square shadow represent the PDCCH, the squares filled with aligned square shadow represent wasted resources and the vertical stripes represent interference.
In the current method for implementing the relay station downlink cooperation, the change of the quantity of the radio resources available for the retransmission data cannot be acquired by the relay station, thus the corresponding physical layer processing cannot be performed normally during retransmission, which, as shown in FIG. 4, may result in interference between the retransmission signals, or waste of the radio resources, or even retransmission failure, and the system performance may be reduced.
Currently, the proposal put forward to solve the aforementioned problems is shown as FIG. 5, which shows a schematic diagram of relay station downlink cooperative retransmission based on signaling control in the prior art. The base station informs the relay station of how to perform retransmission or the condition of the available radio resources on the retransmission sub-frame in advance by a control signaling on a certain control sub-frame, then the relay station performs the corresponding physical layer processing for a Transport Block (TB) to be retransmitted according to the control signaling received from the base station and performs cooperative retransmission on the retransmission sub-frame.
In the method shown as FIG. 5, the base station is required to send a control signaling to the relay station before performing the cooperative retransmission, which undoubtedly induced extra overhead. Furthermore, the relay station is required to receive the control signaling on a certain control sub-frame, however, in order to avoid self-interference, the control sub-frame cannot be configured as a cooperative retransmission sub-frame of other users, thus greatly influencing the flexibility of sub-frame configuration. In addition, the base station is required to begin to generate the control signaling and transmit it only after the condition of the available radio resources on the retransmission sub-frame is determined, and the relay station is required to begin the corresponding physical layer processing and performs the retransmission only after receiving and correctly decrypting the control from the base station, thereby resulting in a great amount of time delay and largely reducing the service quality and the resource utilization rate.